Cigarette filters now in commercial use are only partially effective; they remove approximately 30% of the tars and nicotine. The approximately 70% that passes the filter obviously is not trapped by the filter material. The reason is that these substances are in the form of fine particles which are colloidally dispersed, and because of their small size pass through the usual or known filters with the gases in which they are dispersed.
Tobacco smoke is a two-phase system: a vapor phase and a dispersed particulate phase. The vapor phase may be considered the fraction which is volatile about 86.degree. F., which is smoking temperature, and some high boiling point components not immediately condensed. The smoke consists of approximately 4-9% particulate matter of particles dispersed in the 91-96% vapor phase components. The vapor phase components consist of nitrogen, oxygen, carbon monoxide gases and other materials which are in the gaseous state about 86.degree. F. During the smoking process, pyrosynthesis, pyrolysis, and distillation take place, and it has been estimated that there are as many as 700-800 resulting compounds. Straight chain hydrocarbons predominate.
When a cigarette is being smoked, the particulates which are generated have Brownian movement within the gaseous vapor phase. Observations with a dark field condenser, dialysis, electrophoresis, and Tyndal studies indicate that many particulates in the smoke are negatively charged and have lively Brownian motion. It has been estimated that there are approximately 2.times.10.sup.9 negatively charged particles per millimeter in tobacco smoke.
Also, one of the serious problems in the filtration of tobacco smoke is the hydrophobic character of the carcinogenic tars, which are oleophilic. A wet filter will not hold on its surface the particulates having a hydrophobic character.
In Striefling U.S. Pat. No. 2,181,614; Nov. 28, 1939, a cigarette filter is disclosed which comprises a porous substrate impregnated with an oxide or hydroxide of calcium, magnesium, aluminum or silicon, including aluminum oxide in colloidal form. The colloidal alumina, however, is made by a wet process as distinguished from the dry process and is in amorphous form. Also, the impregnated filter medium is definitely alkaline. Reliance is placed upon the porous or highly absorptive structure of the described filter medium for the mechanical absorption and chemical neutralization of the nicotine vapors and acid fumes.